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Bidelman G, Sisson A, Rizzi R, MacLean J, Baer K. Myogenic artifacts masquerade as neuroplasticity in the auditory frequency-following response (FFR). BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.10.27.564446. [PMID: 37961324 PMCID: PMC10634913 DOI: 10.1101/2023.10.27.564446] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2023]
Abstract
The frequency-following response (FFR) is an evoked potential that provides a "neural fingerprint" of complex sound encoding in the brain. FFRs have been widely used to characterize speech and music processing, experience-dependent neuroplasticity (e.g., learning, musicianship), and biomarkers for hearing and language-based disorders that distort receptive communication abilities. It is widely assumed FFRs stem from a mixture of phase-locked neurogenic activity from brainstem and cortical structures along the hearing neuraxis. Here, we challenge this prevailing view by demonstrating upwards of ~50% of the FFR can originate from a non-neural source: contamination from the postauricular muscle (PAM) vestigial startle reflex. We first establish PAM artifact is present in all ears, varies with electrode proximity to the muscle, and can be experimentally manipulated by directing listeners' eye gaze toward the ear of sound stimulation. We then show this muscular noise easily confounds auditory FFRs, spuriously amplifying responses by 3-4x fold with tandem PAM contraction and even explaining putative FFR enhancements observed in highly skilled musicians. Our findings expose a new and unrecognized myogenic source to the FFR that drives its large inter-subject variability and cast doubt on whether changes in the response typically attributed to neuroplasticity/pathology are solely of brain origin.
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MacLean J, Stirn J, Sisson A, Bidelman GM. Short- and long-term neuroplasticity interact during the perceptual learning of concurrent speech. Cereb Cortex 2024; 34:bhad543. [PMID: 38212291 PMCID: PMC10839853 DOI: 10.1093/cercor/bhad543] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2023] [Revised: 12/20/2023] [Accepted: 12/21/2023] [Indexed: 01/13/2024] Open
Abstract
Plasticity from auditory experience shapes the brain's encoding and perception of sound. However, whether such long-term plasticity alters the trajectory of short-term plasticity during speech processing has yet to be investigated. Here, we explored the neural mechanisms and interplay between short- and long-term neuroplasticity for rapid auditory perceptual learning of concurrent speech sounds in young, normal-hearing musicians and nonmusicians. Participants learned to identify double-vowel mixtures during ~ 45 min training sessions recorded simultaneously with high-density electroencephalography (EEG). We analyzed frequency-following responses (FFRs) and event-related potentials (ERPs) to investigate neural correlates of learning at subcortical and cortical levels, respectively. Although both groups showed rapid perceptual learning, musicians showed faster behavioral decisions than nonmusicians overall. Learning-related changes were not apparent in brainstem FFRs. However, plasticity was highly evident in cortex, where ERPs revealed unique hemispheric asymmetries between groups suggestive of different neural strategies (musicians: right hemisphere bias; nonmusicians: left hemisphere). Source reconstruction and the early (150-200 ms) time course of these effects localized learning-induced cortical plasticity to auditory-sensory brain areas. Our findings reinforce the domain-general benefits of musicianship but reveal that successful speech sound learning is driven by a critical interplay between long- and short-term mechanisms of auditory plasticity, which first emerge at a cortical level.
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Affiliation(s)
- Jessica MacLean
- Department of Speech, Language and Hearing Sciences, Indiana University, Bloomington, IN, USA
- Program in Neuroscience, Indiana University, Bloomington, IN, USA
| | - Jack Stirn
- Department of Speech, Language and Hearing Sciences, Indiana University, Bloomington, IN, USA
| | - Alexandria Sisson
- Department of Speech, Language and Hearing Sciences, Indiana University, Bloomington, IN, USA
| | - Gavin M Bidelman
- Department of Speech, Language and Hearing Sciences, Indiana University, Bloomington, IN, USA
- Program in Neuroscience, Indiana University, Bloomington, IN, USA
- Cognitive Science Program, Indiana University, Bloomington, IN, USA
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MacLean J, Stirn J, Sisson A, Bidelman GM. Short- and long-term experience-dependent neuroplasticity interact during the perceptual learning of concurrent speech. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.09.26.559640. [PMID: 37808665 PMCID: PMC10557636 DOI: 10.1101/2023.09.26.559640] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/10/2023]
Abstract
Plasticity from auditory experiences shapes brain encoding and perception of sound. However, whether such long-term plasticity alters the trajectory of short-term plasticity during speech processing has yet to be investigated. Here, we explored the neural mechanisms and interplay between short- and long-term neuroplasticity for rapid auditory perceptual learning of concurrent speech sounds in young, normal-hearing musicians and nonmusicians. Participants learned to identify double-vowel mixtures during ∼45 minute training sessions recorded simultaneously with high-density EEG. We analyzed frequency-following responses (FFRs) and event-related potentials (ERPs) to investigate neural correlates of learning at subcortical and cortical levels, respectively. While both groups showed rapid perceptual learning, musicians showed faster behavioral decisions than nonmusicians overall. Learning-related changes were not apparent in brainstem FFRs. However, plasticity was highly evident in cortex, where ERPs revealed unique hemispheric asymmetries between groups suggestive of different neural strategies (musicians: right hemisphere bias; nonmusicians: left hemisphere). Source reconstruction and the early (150-200 ms) time course of these effects localized learning-induced cortical plasticity to auditory-sensory brain areas. Our findings confirm domain-general benefits for musicianship but reveal successful speech sound learning is driven by a critical interplay between long- and short-term mechanisms of auditory plasticity that first emerge at a cortical level.
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Rizzi R, Bidelman GM. Duplex perception reveals brainstem auditory representations are modulated by listeners' ongoing percept for speech. Cereb Cortex 2023; 33:10076-10086. [PMID: 37522248 PMCID: PMC10502779 DOI: 10.1093/cercor/bhad266] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2023] [Revised: 06/27/2023] [Accepted: 07/10/2023] [Indexed: 08/01/2023] Open
Abstract
So-called duplex speech stimuli with perceptually ambiguous spectral cues to one ear and isolated low- versus high-frequency third formant "chirp" to the opposite ear yield a coherent percept supporting their phonetic categorization. Critically, such dichotic sounds are only perceived categorically upon binaural integration. Here, we used frequency-following responses (FFRs), scalp-recorded potentials reflecting phase-locked subcortical activity, to investigate brainstem responses to fused speech percepts and to determine whether FFRs reflect binaurally integrated category-level representations. We recorded FFRs to diotic and dichotic stop-consonants (/da/, /ga/) that either did or did not require binaural fusion to properly label along with perceptually ambiguous sounds without clear phonetic identity. Behaviorally, listeners showed clear categorization of dichotic speech tokens confirming they were heard with a fused, phonetic percept. Neurally, we found FFRs were stronger for categorically perceived speech relative to category-ambiguous tokens but also differentiated phonetic categories for both diotically and dichotically presented speech sounds. Correlations between neural and behavioral data further showed FFR latency predicted the degree to which listeners labeled tokens as "da" versus "ga." The presence of binaurally integrated, category-level information in FFRs suggests human brainstem processing reflects a surprisingly abstract level of the speech code typically circumscribed to much later cortical processing.
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Affiliation(s)
- Rose Rizzi
- Department of Speech, Language, and Hearing Sciences, Indiana University, Bloomington, IN, United States
- Program in Neuroscience, Indiana University, Bloomington, IN, United States
- School of Communication Sciences and Disorders, University of Memphis, Memphis, TN, United States
| | - Gavin M Bidelman
- Department of Speech, Language, and Hearing Sciences, Indiana University, Bloomington, IN, United States
- Program in Neuroscience, Indiana University, Bloomington, IN, United States
- Cognitive Science Program, Indiana University, Bloomington, IN, United States
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Rizzi R, Bidelman GM. Duplex perception reveals brainstem auditory representations are modulated by listeners' ongoing percept for speech. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.05.09.540018. [PMID: 37214801 PMCID: PMC10197666 DOI: 10.1101/2023.05.09.540018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
So-called duplex speech stimuli with perceptually ambiguous spectral cues to one ear and isolated low- vs. high-frequency third formant "chirp" to the opposite ear yield a coherent percept supporting their phonetic categorization. Critically, such dichotic sounds are only perceived categorically upon binaural integration. Here, we used frequency-following responses (FFRs), scalp-recorded potentials reflecting phase-locked subcortical activity, to investigate brainstem responses to fused speech percepts and to determine whether FFRs reflect binaurally integrated category-level representations. We recorded FFRs to diotic and dichotic stop-consonants (/da/, /ga/) that either did or did not require binaural fusion to properly label along with perceptually ambiguous sounds without clear phonetic identity. Behaviorally, listeners showed clear categorization of dichotic speech tokens confirming they were heard with a fused, phonetic percept. Neurally, we found FFRs were stronger for categorically perceived speech relative to category-ambiguous tokens but also differentiated phonetic categories for both diotically and dichotically presented speech sounds. Correlations between neural and behavioral data further showed FFR latency predicted the degree to which listeners labeled tokens as "da" vs. "ga". The presence of binaurally integrated, category-level information in FFRs suggests human brainstem processing reflects a surprisingly abstract level of the speech code typically circumscribed to much later cortical processing.
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Affiliation(s)
- Rose Rizzi
- Department of Speech, Language, and Hearing Sciences, Indiana University, Bloomington, IN, USA
- Program in Neuroscience, Indiana University, Bloomington, IN, USA
- School of Communication Sciences and Disorders, University of Memphis, Memphis, TN, USA
| | - Gavin M. Bidelman
- Department of Speech, Language, and Hearing Sciences, Indiana University, Bloomington, IN, USA
- Program in Neuroscience, Indiana University, Bloomington, IN, USA
- Cognitive Science Program, Indiana University, Bloomington, IN, USA
- School of Communication Sciences and Disorders, University of Memphis, Memphis, TN, USA
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Bidelman GM, Carter JA. Continuous dynamics in behavior reveal interactions between perceptual warping in categorization and speech-in-noise perception. Front Neurosci 2023; 17:1032369. [PMID: 36937676 PMCID: PMC10014819 DOI: 10.3389/fnins.2023.1032369] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2022] [Accepted: 02/14/2023] [Indexed: 03/05/2023] Open
Abstract
Introduction Spoken language comprehension requires listeners map continuous features of the speech signal to discrete category labels. Categories are however malleable to surrounding context and stimulus precedence; listeners' percept can dynamically shift depending on the sequencing of adjacent stimuli resulting in a warping of the heard phonetic category. Here, we investigated whether such perceptual warping-which amplify categorical hearing-might alter speech processing in noise-degraded listening scenarios. Methods We measured continuous dynamics in perception and category judgments of an acoustic-phonetic vowel gradient via mouse tracking. Tokens were presented in serial vs. random orders to induce more/less perceptual warping while listeners categorized continua in clean and noise conditions. Results Listeners' responses were faster and their mouse trajectories closer to the ultimate behavioral selection (marked visually on the screen) in serial vs. random order, suggesting increased perceptual attraction to category exemplars. Interestingly, order effects emerged earlier and persisted later in the trial time course when categorizing speech in noise. Discussion These data describe interactions between perceptual warping in categorization and speech-in-noise perception: warping strengthens the behavioral attraction to relevant speech categories, making listeners more decisive (though not necessarily more accurate) in their decisions of both clean and noise-degraded speech.
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Affiliation(s)
- Gavin M. Bidelman
- Department of Speech, Language and Hearing Sciences, Indiana University, Bloomington, IN, United States
- Program in Neuroscience, Indiana University, Bloomington, IN, United States
| | - Jared A. Carter
- School of Communication Sciences and Disorders, University of Memphis, Memphis, TN, United States
- Hearing Sciences – Scottish Section, Division of Clinical Neuroscience, School of Medicine, University of Nottingham, Glasgow, United Kingdom
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